Page "Welwitschia" Paragraph 2

The taxonomic placement of Welwitschia has changed many times with the development of new classification systems ( see Flowering plants: History of classification ).

Most botanists have treated Welwitschia as a distinct monotypic genus in a monotypic family or even order.

Most recent systems place Welwitschia mirabilis in its own family Welwitschiaceae in the gymnosperm order Gnetales.

The order Gnetales is most closely related to the order Pinales, which includes pines, spruces, larches and firs.

Genetic analyses indicate that the Gnetales arose from within the conifer group, and any morphological similarities between angiosperms and Gnetales are separately derived.

The ancestors of the extant gymnosperm orders-the Gnetales, Coniferales, Cycadales and Ginkgoales-arose during the Late Paleozoic, and became the dominant component of the Late Permian and Mesozoic flora.

Fossil evidence indicates that members of the Welwitschiaceae were present in South America during the Lower Cretaceous ( Mesozoic era ).

Jacobson and Lester suggest that these early habitats of Welwitschiaceae were more mesic than the current desert conditions, and that the present fragmented and isolated population distribution could be attributed to aridification during the Tertiary and Quaternary, which restricted the plants to locales providing sufficient water for their needs.